MIB Browser is selected by default and it shows the MIB tree with its options for SNMP request and OID search.
MIB browser options:
Device mode is used to set the Current device. Any SNMP request in the MIB tab will be sent to the Current device.
On screenshot to the left you can see that the Current device is cisco-xyz. When you click on the Request in the MIB tab, SNMP Query command will be sent to this device.
Device Tab includes following options and information: